This invention concerns methods and apparatus for identifying articles to allow verification and authentication, particularly articles formed predominantly from non-magnetic material and incorporating magnetic fibres having recognisable magnetic properties. The invention is of particular application in the field of high value documents such as original Agreements, bank notes, value coupons, bonds, passports and the like. However the invention is not limited to such documents and is equally applicable to the recognition and authentication of any nonmagnetic article in which identifiable magnetic particles have been embedded.
It has been proposed in EP 96203529.1 filed Dec. 12, 1996 to incorporate magnetic particles of particular shape and magnetic properties as a security feature in articles which need to be recognised. Hitherto the proposal has been linked to the inhibition of photocopying of high value documents such as bank notes by colour copiers and the proposal has been to incorporate a suitable sensor in a colour copier which automatically detects the presence of the magnetic particles or fibres in a document placed on the copying platen. Upon detection of such a document, the sensor is arranged to generate a signal which is utilised within the copier to defeat the copying of the article either by inhibiting the copying function of the machine or degrading the copy so that the article is not reproduced accurately by the copying process.
The detection system on the colour copiers has been achieved with a multi-sensor head mounted on a scanning carriage. The gap between the sensor and the documents is defined from a combination of the glass or platen thickness, a tolerable gap between the scan head and the glass and the depth of focus of the optical system above the glass. This means that the multi-sensor has to work at a distance of a few cm. With the combination of distance and an air core for the magnetic scanning head it was originally noted that with an acceptable coil mass, size and power consumption this would result in a maximum magnetic field, which would mean that the magnetic particles would ideally need to saturate below 1000 A/m, i.e. have a magnetic saturation field Hs below 1000 A/m.
The terms xe2x80x9cmagnetic saturation field Hsxe2x80x9d are herein defined as the applied magnetic field at the onset of saturation of the flux density in the ferro-magnetic particles, above which point the variation of the flux density in the particles with the applied field becomes substantially non-linear. In addition it was noted that saturation at the levels of practicable fields could not be achieved unless the demagnetisation factor N was smaller than {fraction (1/250)}, preferably smaller than {fraction (1/1000)} in order to allow for the typical levels of permeability which result from hard drawing materials such as Permalloy. This meant that long thin particles were needed and that round ones would not be suitable.
The demagnetisation factor N is defined in the following well known formula:
Hin=Happxe2x88x92Nxc3x97M
where M is the magnetisation of the material, Happ is the applied magnetic field, Hin is the magnetic field inside the material and N is the demagnetisation factor.
Summarizing other magnetic propties, the magnetic particles had:
i) a magnetic saturation field Hs being greater than 100 A/m, preferably greater than 200 A/m and most preferably greater than 300 A/m; this lower value is chosen not to trigger off EAS (electronic article surveillance) alarms
ii) a magnetic saturation flux density Bs being greater than 0.1 Tesla;
iii) a magnetic dynamic permeability xcexcd ranging from 10 to 10000. The term magnetic dynamic permeablity xcexcd is defined here as the ratio of the flux density, to the magnetic field times the permeability of free space, at the onset of saturation.
U.S. Pat. No. 5,749,946 discloses a method for checking the authenticity of a security article by detecting the magnetic resonance of an authenticating substance at a resonance frequency.
The sensor proposed for this application is a magnetic field emitting and detection device adapted for xe2x80x9cpoint of transactionxe2x80x9d verification, e.g. where security articles are exchanged for the purpose of goods, services or money. xe2x80x9cPoint of transactionxe2x80x9d locations may be shop tills, Banks and Building Society counters, Ticket issuing offices at railway stations, Bureau de Change, and the like.
An object of the present invention is to provide a compact apparatus which includes a sensing head adapted to be brought into close proximity or actual contact with an article which is to be recognised so that an electrical signal can be generated in response thereto for authenticating the article which is to be presented to the sensing head.
It is also an object of the invention to provide hand held, finger, or thumb mounted devices, for use at point of transaction locations typically in combination with a housing containing a power supply, signal processing and alarm means, for the same purpose.
It is another object of the invention to provide a method of applying a sensor to articles which may or may not contain magnetic fibres or particles to allow an electrical signal to be generated to indicate whether or not the particles are present in the article concerned.
According to one aspect of the invention, there is provided a method for checking the authenticity of a security article containing at least one magnetic element such as magnetic particles having a magnetic saturation field Hs being greater than 100 A/m. The method comprises the following steps:
(a) generating an alternating field of one or more fundamental frequencies with an amplitude being greater than the saturation field of the magnetic element;
(b) subjecting an article to be detected to the field;
(c) detecting a detection signal emanating from the article to be detected;
(d) examining the detection signal for the presence of any particular harmonics of the fundamental frequencies or of any linear combination of the fundamental frequencies and of the harmonics, the particular harmonics or the linear combination being indicative of the presence of the magnetic element as magnetic particles.
Or, viewed from still another angle, there is provided a method of making a verifiable article which is to be detected by subjecting it to an alternating magnetic field to determine whether there is at least one specific harmonic response generated by interaction between the article and the field due to the non linear response of the flux density with the applied field from particles of magnetic material associated with the article. The method is characterised by selecting the magnetic material properties and the shape of the particles so that they have a magnetic saturation field greater than 100 A/m (preferably greater than 300 A/m) so as to prevent triggering off electronic article surveillance (EAS) systems which also include magnetic fields, and incorporating said particles into the said article.
According to another aspect of the present invention, there is provided a system by which security articles can be verified, wherein authentic articles have incorporated therein particles of a selected magnetic material and selected shape, the particles being saturable by an alternating magnetic field thereby to generate at least one harmonic of the fundamental frequency of the alternating field, and wherein a sensor is provided, a first part of which generates a local alternating magnetic field to which articles as aforesaid are to be subjected for verification, and a second part of which generates by induction electric signals indicative of the response of the material making up the article to the said alternating field. Signal analysing means is provided, adapted to determine if a particular frequency, or a spectrum of frequencies, is present in the generated signals. The system is characterised in that the selection of the magnetic material and the selection of the shape of the particles is restricted to particles which require magnetic fields in excess of 100 A/m (preferably in excess of 300 A/m) before they become saturated, to prevent authentic articles as aforesaid from triggering electronic article surveillance alarms, and the first part of the sensor generates a local field of sufficient strength to saturate any such particles if in xe2x80x9cclose proximityxe2x80x9d to, or in contact with, the sensor.
According to still another aspect of the invention, there is provided an apparatus for carrying out a method according to the invention or for use in a system according to the invention.
More particularly, the invention provides a method of checking the authenticity of an article in which a sensor is moved into xe2x80x9cclose proximityxe2x80x9d or contact with the article. A confirmation of authentication signal which may be audible or visible or vibratory or any combination hereof is generated if magnetic particles or fibres having the requisite property are detected as being present in the article.
Within the context of the present invention the terms xe2x80x9cclose proximityxe2x80x9d mean at a distance smaller than 10.0 mm, typically smaller than 2.0 mm, e.g. at a distance smaller than 1.0 mm.
A consequence of this very small distance is that it can be possible to have a design which could even saturate spherical particles, i.e. particles having a demagnetisation factor N smaller than ⅓, e.g. smaller than {fraction (1/20)}.
However, a very important issue for an anti-counterfeit solution is to make the security feature itself as difficult as possible to copy. With the approach proposed in EP 96203529.1, the security feature is an elongated magnetic particle such as a hard drawn metal fibre of a particular composition and of a diameter preferably less than 30 micron. This security feature is much more difficult to imitate than spherical magnetic powders. Moreover, the particular characteristics of the metal fibres enable them to be virtually hidden in a substrate such as paper or plastic, not break out of the substrate with normal flexing usage and life, and which can be made to produce a very characteristic signal. The latter objective is enabled by using material with a particular coercivity, permeability and shape which provides a magnetic saturation field substantially greater than that found in EAS gates and which is substantially less than found with other common objects (including for example magnetic powders.
Therefore, in a preferable embodiment of the present invention, the demagnetisation factor N isxe2x80x94stillxe2x80x94smaller than {fraction (1/250)} and it has been found convenient to limit the magnetic saturation field to approximately 1000 A/m to 2000 A/m at a distance of 1.0 mm above the poles of the sensor head.
The invention also lies in a method of checking the authenticity of an article such as a security document in which the article is moved into close proximity or contact with a sensor or in which the sensor is moved into close proximity or contact with the article.
The invention also lies in a method in which relative movement is introduced between the article and the sensor so that if perchance a region which is devoid of the magnetic particles or fibres is in registry with the sensor, the movement will cause a region which does contain the fibres or particles to be moved into proximity with the sensor either by movement of the sensor relative to the article or by the article relative to the sensor, to allow the authentication signal to be generated.
It is of advantage if the sensor does not have to be any larger than necessary, particularly if it is to be associated or incorporated in a till or if it is to be incorporated in a hand-held device equivalent to a pen, and since the distribution of the magnetic particles or fibres throughout the article may not be uniform, the method involving relative movement, between the sensor and the article overcomes the possible problems associated with viewing only a restricted area of the article by a small sensor.
The method of the invention is of primary application in the authentication of bank notes which have been printed on sheet material containing the said magnetic fibres or particles. However the invention is not limited to bank notes and the method of the invention is equally applicable to the authentication of any article formed from non-magnetic material containing the magnetic particles or fibres having the special magnetic properties.
In each of the methods as aforesaid, the sensor comprises a transmitting device which generates an alternating magnetic field of one or more fundamental frequencies and a detection system having an enhanced response to magnetic field variation at a frequency which is a harmonic of the fundamental frequencies or of any linear combination of the fundamental frequencies of the transmitted alternating field, and which is a predominant component of a secondary magnetic field generated by the magnetic particles or fibres as a result of a non-linear magnetic response of the material forming the particles or fibres to the transmitted alternating magnetic field.
The preferred method of the invention thus comprises the steps of generating a primary alternating magnetic field at a first frequency, introducing into a region containing a concentration of magnetic flux of the first alternating field an article containing at least one magnetic element having a non-linear magnetisation response to magnetic field changes at the frequency of the alternating field, thereby to introduce a secondary field variation at at least one harmonic of the fundamental frequency, into the magnetic field, detecting the secondary magnetic field variation generated by the non-linear response of the magnetic element to the changes of field due to the primary alternating field, generating electrical signals at the harmonic frequency due to the secondary magnetic field generated by the said non-linear response, selectively processing electrical signals generated by the harmonic frequency field and characteristic of the non-linear response, as opposed to electrical signals generated by the primary alternating magnetic field, detecting for the presence of electrical signals at the said harmonic frequency and generating a signal if such signals are detected.
An authentication signal can thus be generated if the relevant harmonic is detected in the processed signal, and the absence of any such harmonic will result in no authentication signal being generated, which can be taken to indicate that there are no appropriate magnetic elements (such as fibres or particles) within the article.
According to a preferred feature of the method, inductor means is provided proximate to an article to be detected and a generally sinusoidal electric current is caused to flow in the inductor means to generate a primary sinusoidally varying magnetic field which links the article proximate thereto, input signals for the selective signal processing system are derived from the inductor means, and the signal processing system is adjusted so as not to respond to electrical signals at the fundamental frequency of the sinusoidal alternating current producing the primary magnetic field, or low harmonics thereof, but to be significantly responsive to electrical signals at frequencies equivalent to at least one selected higher harmonic of the said alternating current frequency. Magnetic particles or fibres situated in the primary magnetic field are detectable if they have a non-linear magnetic response at the fundamental frequency so as to generate a secondary varying magnetic field at the selected higher harmonic to which the signal processing system is responsive, provided the inductor means is also linked by magnetic flux of the secondary magnetic field generated by the non-linear response of the particles in the fibres.
In one method the inductor means comprises at least two separate windings and the primary magnetic field producing alternating electric current is supplied to one of the windings and at least one secondary winding intimately associated with the primary winding provides electrical signals for the signal processing system due to voltages induced by a linking of the secondary winding by the secondary magnetic flux generated by the non-linear response particles or fibres in the article under test.
In a second method, a single winding may be used to which the primary alternating current is supplied for generating the primary field and from which electrical signals are delivered to the processing system, which by virtue of its response, will not respond significantly to electrical signals at frequencies close to the primary current frequency, but will respond to higher harmonics which will only be present if fibres or particles having the particular non-linear characteristic are linked by the alternating magnetic flux generated by the primary currents.
The invention also lies in a sensor and an apparatus for performing the invention as aforesaid.
In one embodiment of such an apparatus, a platform is provided on which an article can be placed for checking, the platform incorporating at least one sensor for generating and transmitting a primary alternating magnetic field towards and into the article and for responding to the secondary alternating magnetic field returning from the article. The alternating magnetic field returning from the article has a frequency component significantly higher than the frequency of the field transmitted to the article. Signal processing circuit means is provided responsive to electrical voltages induced by the returning flux at said higher frequency and which is adapted to respond predominantly to signals at that frequency to generate an authentication signal. This will only occur if magnetic flux at that frequency is present in the sensor due to the returning magnetic field generated by the non linear response of the magnetic particles or fibres to the primary field. The invention could also make use of more than one of the harmonic frequencies generated by the magnetic particles or fibres to improve sensitivity or aid in the discrimination of forgeries which try to copy the magnetic characteristics of the particle or fibres described in this application.
Where the sensor is very small in cross-sectional area so that only a small area of the article registers therewith, means may be provided for moving the sensor relative to the platform (and therefore the stationary article thereon) to enable different regions of the article to be detected by the sensor during a single test.
Alternatively the platform may be such that an article can be moved across the surface thereof in a wiping action, such that a surface of the article is in close proximity with, if not in contact with the sensor located therein. In this way different regions of the article will be presented in succession to the sensor without the need for the sensor to be moved relative to the platform or the article thereon. This is of particular value where the article is a flexible sheet material such as a bank note.
The platform is conveniently formed from a thin non-magnetic, e.g. plastic, sheet or membrane over the pole pieces of the sensor. Alternatively the pole pieces themselves could form the platform. In a preferred embodiment the platform is part of, or all of, the surface of a small box which may contain the signal processing electronics and the indicator which is activated if the higher harmonic magnetic flux is detected due to the presence of magnetic fibres or particles in the article under test. The indicator could be a sounder, or a lamp or both. The box could contain its own power supply or be supplied from an external source.
In another embodiment of the invention, a sensor may be located in the end of an elongated pen-like member which can be held between finger and thumb in the manner of a writing instrument and can be drawn across the surface of an article to be detected as if the sensor were being used to draw a line across the said surface.
In one embodiment the invention can thus be said to provide a sensor pen which can be picked up and used to check an article as aforesaid, and such a sensor pen may include a push button switch for activating the device so that the sensing of an article is restricted to when the button is depressed, for example by the user""s forefinger.
The elongate pen-like device may serve to house electric circuit means associated with the selective signal processing or vibrator system, and a sounder, or lamp, or both, which is or are activated if the higher harmonic magnetic flux is detected due to the presence of magnetic fibres or particles in the article under test. The elongate member may also incorporate an own supply such as a battery for powering the device.
Alternatively the sensor pen may be connected by a cable to a subsidiary unit which may be a separate box containing power supply and/or electronics and/or sounder and/or lamp, and may be a device such as a cash register, or computer as used by a cashier in a bank or building society.
Alternatively the sensor may comprise a document screening device in the form of a cheque reader or the like to which a document such as a passport can be presented.
Where it is permissible to make contact with the surface of the article and to allow light pressure to be exerted thereon, the sensor may be mounted in a separate housing which is resiliently movable relative to a main housing, and switch means is operable from an open to a closed condition by relative movement of the sensor housing as will occur if the sensor housing is pressed lightly into contact with an article to be detected or vice versa. In this way the user does not have to depress a switch to render the device operational. The switch may comprise mechanical contacts or may be a capacitive switch which consumes little power. Since it is important that the switch is closed for the device to function correctly, the device may be adapted to produce a first tone or illuminate a first lamp when the switch is closed, and to generate a second tone in place of the first tone (or second lamp in place of the first lamp) if signals at the selected higher harmonic or harmonics of the fundamental frequency are detected by the signal processing system. The user is thus instructed by the tone or lamps as to whether or not the device is sensing the presence of appropriate fibres or particles and whether or not it is necessary to shift the device over the surface of the article in order to try and find particles or fibres within the article under test.
Utilising such a sensor, the user can be instructed to listen for a first tone and to move the sensor over the article and listen for the second tone. Only if the second tone is produced will the article be authenticated by the user.
The method is relatively fail-safe since if the first tone is not produced, the test cannot be performed in the first place, and the change from the first tone to the second tone will only occur in the presence of appropriate particles or fibres.
Preferably the first tone is at the first relatively low pitch and the second tone is at a relatively higher pitch so that it is impossible for the user to mistakenly assume that the second tone has been produced.
According to a preferred feature of this aspect of the invention, the first tone is generated for a set period of time before the second tone can be generated even if appropriate harmonic content is detected by the signal processing system, so that the user has to listen for the first tone, before the second tone can be generated and can be heard.
According to another feature of this aspect of the invention, the second tone may be generated at a considerably greater power level than the first tone so that even in a relatively noisy environment, the second tone will be heard.
The invention is of particular application in the field of bank note checking and since these are regularly handled by a cashier wearing a thumb or finger stall, according to another aspect of the invention, a sensor as aforesaid may be incorporated in a thumb stall or finger stall which may also incorporate a miniature signal processing system and signalling device, or be connected to same, as in a wrist band to indicate when magnetic particles or fibres are present in a bank note contacted by the stall. The secondary unit housing the electronics and power supply may include audible, visual or vibratory alarms. The electronics and alarms may instead or in addition be incorporated into other equipment normally associated with the cashiers position, such as a computer or till or cash register.
Since the finger or thumb stall is of necessity brought into contact with a note in use, pressure sensitive switch means may also be incorporated in the stall as aforesaid, and an audible tone or vibration generated or a lamp illuminated in response to the detection by the sensor located in the stall of appropriate magnetic fibres or particles within the note in contact therewith.
In accordance with another feature of this aspect of the invention, the signal processing system to a thumb or finger stall may alternatively generate an inverse of the authentication signal hitherto proposed such that if the stall is in contact with a note which contains appropriate particles or fibres, no audible tone is produced by a sounder associated therewith (or with secondary apparatus to which it is linked), but in the event that the stall is pressed against a note which does contain such fibres or particles, an alarm signal is generated. In this way the operator is not subjected to continual tones which otherwise would be generated every time a genuine note is touched by the stall, but will only be alerted when the stall is brought into contact with a note which does not generate the appropriate response and may therefore be counterfeit note.
In accordance with a further modification of the invention, the pressure sensitive switch means associated with the sensor may be arranged to extinguish a red light and illuminate an orange light when the sensor is first pressed into contact with an article to be tested. The orange light is then extinguished and a green light is produced in the event that appropriate particles or fibres are located as being present in the article, as a visual confirmation of the authenticity of the article. An alarm signal is generated in the event that with continued pressure, no particles or fibres are sensed and the orange light is not extinguished after a given period of time.
According to a preferred feature of the invention, the particles are in fact elongate fibres and during manufacture of the article the fibres are arranged so as to be substantially co-planar. Additionally the fibres may be orientated in a particular manner so that they are not only all in the same plane, but all extend parallel or perpendicular to particular directions within that plane, so that two levels of authentication can be provided, a first which merely detects whether or not the fibres are present, and a second which determines the orientation of the fibres relative to the article.
Alternatively more than two levels of identification can be incorporated with the addition of magnetic particles or fibres having a saturation field greater than 100 A/m but with sets of different magnetic properties e.g. saturation field strength, coercivity or dynamic permeability.
This latter may be of advantage for authenticating specific value documents such as different denomination bank notes, by arranging that the fibres are orientated in different directions within the sheet material, from which the bank notes are produced.
Whether or not the fibres are orientated in parallel to one direction or not, where they are substantially co-planar, albeit randomly dispersed therein, the alternating magnetic field produced by the sensor is advantageously arranged so that the magnetic field generated by an alternating electric current is orientated substantially in the plane in which the magnetic fibres have their major axes, and the detector system associated with the sensor is arranged to pick up emissions from the magnetic fibres as they are driven through the non-linear region of their B-H curve by the alternating magnetic field.
Alternatives to inductive coils for detecting magnetic fields produced include Hall effect, magneto-resistive, magneto-inductive, flux-gate and magneto-impedance sensors. These have an advantage over inductive coils where the frequencies to be detected are low, as these alternatives have a frequency response extending down to 0 Hz.
In one embodiment of sensor, an inductor is provided comprising a coil wound around the central section of a ferrite core having a so-called E section.
In another preferable embodiment, a so-called pot core is employed, in which comprises a cylindrical ferrite cup incorporating a central ferrite core which has the coil wound around it. In both cases (the E-section and the pot core) where two or more windings are required, these are all located on the central section.
The advantage of the E core and pot core design is that they produce a concentration of magnetic flux in a plane just above the exposed end of the central core, so that magnetic flux bridging between the central core and the outer ferrite section will be most concentrated in a plane parallel to the open end of the pot core. Advantageously sheet material such as a bank note or other document to be detected, is located in that plane.
The ferrite material from which the core and surrounding pot are formed is preferably selected so that it limits and preferably minimises the generation of harmonics of the fundamental drive field.
According to another aspect of the invention, the signal processing system incorporates a narrow bandpass filter restricted to one or more of the higher harmonics of the drive magnetic field. Typically one of the harmonics is isolated by the use of such a narrow bandpass filter.
According to a preferred feature of the invention, a surface acoustic wave filter such as is commonly used in radios may be incorporated in the signal processing system.
The latter signal processing system advantageously may in addition to or instead of the acoustic wave filter incorporate a phase sensitive detector using a reference frequency locked to the primary drive field frequency so ast to produce maximum rejection of unwanted frequencies and maximum separation of desired harmonics.
Apparatus embodying the invention may be incorporated into a cash register or till, or computer terminal as provided to a teller or clerk in a building society or bank.
The invention thus also lies in a cash register or till or computer terminal when modified to include a document reader adapted to sense the presence within a document presented thereto of specific magnetic fibres or particles having a non-linear magnetic response to alternating magnetic flux at particular frequencies so as to generate in response thereto magnetic flux at one or more harmonics of the frequency of the energising magnetic field.
An embodiment of the invention also lies in the provision of a datalink to a central computer by which information identifying the document such as denomination and serial number can be stored against time and date, and till, or address, at which the forged document has been submitted, and which may also include details of the person tendering the forged note. This information may be entered by the bank clerk or cashier, or may be an electronic photographic representation of the person taken by a hidden camera such a miniature CCD TV camera located adjacent the till or cash point so that an electronic image of the person tendering the forged note can be obtained and transmitted to the central computer and stored in association with the other data relating to the transaction.